Recently, from the viewpoint of preventing world warming, it has been demanded to reduce the amount of generated CO2 on a global scale. At the congress of the world warming prevention which took place at Kyoto in December 1997, a protocol for the reduction of the exhaust gas was adopted. This protocol established a reduction target in 2010, aiming at reducing at least 5% of a standard with respect of 1990 of the exhaust amounts of greenhouse effect gases (CO2, CH4, N2O and others) of all advanced countries. In accordance with the protocol, Japan has been assigned a duty of lowering 6% of the amount of issuing exhaust gases.
CO2 accounts for 64% of the contribution degree per the greenhouse effect gas with respect to world warming, and is mainly exhausted by using fossil fuel. In Japan, 95% of the greenhouse effect gas generated by social or economical activities is CO2, and more than 90% thereof is accompanied with use of energy. Accordingly, a measure for preventing the world from warming will be to chiefly control CO2 exhausted in conjunction with the use of energy.
With respect to the control of exhausting CO2 accompanied with the use of energy, for example, the iron and steel business world which accounts for about 11% of the final energy consumption of Japan, projects a self-imposed behavior plan toward 2010, and proclaims in this plan a 10% reduction, in comparison with 1990 of the energy consumption in the production process in 2010. Further, as an actual measure thereto other than energy reduction, included are the blowing of waste plastics as reducing agents into blast furnaces, usage of non-used energy in neighboring areas, or contribution to energy saving by making products or by-products.
However, in the present high degree industrialized society, there is per se a limit in the control of using energy which is related to the cutting of the exhaust of CO2, and it is not always easy to accomplish a target of cutting CO2 exhaust only with the control of the amount of energy used.
Accordingly for accomplishing the target of cutting CO2 exhaust, it is considered to be necessary to take such a measure from both sides of cutting the CO2 generated amount, as well as removing CO2 from the generated gas (exhaust gas) However, an effective method which removes CO2 from the exhaust gas on an industrial scale is not yet conventionally known.
As a part of usefully using slag generated in the iron and steel making process, it has been tried to make use of the slag as a seawater immersion block for algae planting places or fish gathering rocky places.
As main embodiments of utilizing slag as such materials, there is a method of utilizing massive slag for algae planting places as it is, and another method of utilizing slag as agglomerates for fish gathering rocky places. However these methods are involved with problems as discussed herein.
In the former method, Ca content contained in slag is dissolved into the sea to probably heighten the pH in the neighboring seawater. The obtained massive slag in the iron-steel making process is suited as a block for such as algae planting places due to surface properties in comparison with concrete products. However, as a block for the algae planting places, the massive slag has functions (adhering property of sea algae or rearing property) only of a similar degree to a natural block, and does not have a special function of accelerating the growing of sea algae.
The slag generated in the iron-steel making process contains much iron content such as metals (grain iron), and ordinarily it is broken to desired sizes for recovering the iron content in the slag for recycle in the iron-steel making process. Slag for algae planting places necessitates sizes of a certain degree, and slag broken for recovering the metal is scarcely used. If use is made of the massive slag as a block for algae planting places, the recovery of the metal useful as iron and steel sources can hardly be practiced.
In contrast, if massive slag containing much metal is immersed into the sea as it is for use as a block in algae planting places, the iron content in the slag is oxidized, depending on sea areas, to cause a shortage of oxygen in the seawater, and further by dissolution of the iron content; the iron content might be excessively supplied in the sea water. For avoiding such problems, the metal in the slag should be perfectly removed. Since the slag content and the metal generally exist in a mixture as if entwined, the slag must be more finely pulverized than the case of the above mentioned metal recovery in order to completely remove the metal. Such finely pulverized slag cannot be used as materials to be immersed in the sea water for the algae planting places.
On the other hand, the latter method uses slag as an agglomerate of a concrete made pre-cast body, and so there seldom occurs a problem of the case that the massive slag is immersed in the sea as it is. However materials available by this method are concrete products whose surfaces are composed of cement mortar, and which therefore cannot exhibit even the properties of massive slag (for example, uneven surface property) which are expected to display performance per se as for algae planting places.
Recently, there has arisen a tendency towards maintenance and improvement of natural circumstances of rivers including living circumstances of creatures such as fishes or shells, and as a part of the tendency, for example, it has been tried to repair riverbeds to be suited to water living creatures (fishes, shells, water insects and others) or water plants (algae, water grass and others) to inhabit and live. In the rivers, creatures' living and resting spaces called biotopes are created with blocks and, accordingly, much uneven riverbeds made by blocks are better for water living creatures. Relatively large spaces among immersed or half-immersed massive blocks on the riverbeds or small spaces among small blocks laid thereon are important living spaces (biotopes) for water living creatures. Blocks on the riverbeds are also places for water plants to live, and for rearing water plants. Blocks are therefore important.
For repairing riverbeds as a part of maintenance or improvement of the natural circumstances of rivers, the sinking or laying of blocks in appropriate forms (for example, placing of large massive blocks, sinking or laying of middle massive or small blocks on the riverbeds) may be a useful means for arranging the circumstances for fish to live or inhabit. For repairing riverbeds, enormous amount of blocks are required. It probably causes destruction of nature to supply natural blocks from other places, and since natural blocks are not cheap, the construction cost is increased.
For usefully using slag generated in the iron and steel making process, it has been tried to utilize slag as sea water immersion blocks for fish gathering rocky places. Concerning blocks for sinking in rivers, slag generated in the iron and steel-making process should be considered.
As discussed hereinabove, with respect of main embodiments for utilizing slag to be immersed in rivers, there is considered a method of using the slag as it is as an immersion block and another method of using the slag as concrete pre-cast agglomerates.
However these methods have problems as discussed hereinabove.
In the former method, the Ca content in the slag is dissolved into the water to probably heighten the pH in the river water. Since the slag generated in the iron and steel making process contains much metal (grain iron), if massive slag is immersed in the water as it is, grain iron is oxidized, and depending on water ranges, a shortage in oxygen might occur in neighboring rivers. For avoiding such problems, the metal in the slag should be completely removed. Since the slag content and the metal generally exist in a mixture as if entwined, the slag must be more finely pulverized than in the case of the above mentioned metal recovery in order to completely remove the metal. Such finely pulverized slag cannot be used as materials to be immersed in the sea water for algae planting places.
On the other hand, as in the latter method, if the slag is used as an agglomerate of a concrete made pre-cast body, since the base is made of concrete, the properties of the massive slag (for example, uneven surface property) which are expected to display performance as an immersion block in the rivers cannot be displayed. The concrete has a high pH (ordinarily, about a pH of 12 to 12.5), so that it increases the pH in the neighboring river water or delays growth of algae.
It has recently been recognized to prepare fish ways for fishes to move to upstream or downstream or to go up in dams or barrages, and repairs therefore have been carried out. The fish way is provided with a waterway (usually, having a width of about 2 to 5 m) for forming flows for fish to move in parts of the dam or barrage, and known are slant paths or stepwise paths. Conventionally ordinary fish ways are made by cutting parts of the dam or barrage in the water path encircled with the concrete.
Thus, the conventional fish way has no obstacle for fish to move as long as no problems exist in water flowing speed, water bottom obliquity or steps. However, since the concrete-made fish way has a smooth bottom, it is difficult for water living creatures such as algae to live, and there are problems for water living plants (for example, crusts or water living insects) relating to moving because of the catching with their claws on the riverbed (surface projections as a block for water living plants). For these problems, there is a method of structuring the fish way with a foam concrete to make fine indentations on the bottom of the fish way, however the construction cost is high with less practicability. In either way, the concrete has a high pH, which is not preferable for water living creatures moving on the riverbed.
Algae planting places are for breeding sea living plants and creatures in coastal and sea areas, and are indispensable as living places for useful fish and shellfish, rearing marine algae, laying eggs of fish and shellfish, breeding fry and small fish, or baiting. In addition, recently, nitrogen or phosphorus in the seawater are taken in by marine algae or other living creatures through the food cycle or chain in the algae planting places, otherwise suspension materials subside in the algae planting places. Thus, a water purifying action has been noticed.
However, nowadays, the algae planting places continue to rapidly fade or decline by influences of reclaiming coasts or corruption of the seawater. In particular, recently, in many coastal or sea areas, a big problem of so-called “shore burn” phenomena occurs. It has therefore been demanded to establish an algae place creation act for recovering algae planting places.
Algae creating methods conventionally carried out are roughly divided in the following two ways.
(1) At places where algae planting places are desired, bases for rearing marine algae (mainly, natural blocks or concrete blocks) are laid, and seeds and saplings of marine algae or mother algae are transplanted, and managed for rearing them as required.
(2) Places environmentally easy to become algae living places, that is, such places suitable for creating the algae places in view of circumstances as water depth, water quality or ocean current, which are within reach of spores of marine algae from existing algae places, are selected, and the bases are laid there. Algae places are thus created which are maintenance free (transplanting or rearing managing are not basically done).
Of these methods, the method (1) is advantageous in wide selecting ranges for creating the algae places, however, basically all of the creations are artificial, and it is necessary to fully manage taking-roots or rearing of transplanted seeds and saplings, for which a lot of time and tremendous cost are taken. This method is absolutely unsuited to large scale creations of algae places.
On the other hand, as the method (2) creates algae places which are maintenance free, other than laying the bases, it is advantageous in that it takes less time and cost, in comparison with the method (1). However, this method is short with respect of general purpose uses because of limited places to become algae places. According to a certain report for creating an algae place by the method (2), at a proper period in a place which does not naturally become an algae place, it is preferable to select a place within 100 m from an existing algae place, taking into consideration the reach of spores or seeds from existing algae places. Accordingly, it is assumed that this method is difficult to create algae places at places where circumferentially whole algae places have been faded by shore burn.